1. Field of the Invention
The present invention relates to an apparatus for wet desulfurization of flue gases. In more details, it relates to an economical wet type flue gas desulfurization apparatus characterized by relatively low equipment and operation costs.
2. Description of Related Art
In order to achieve high sulfur removal efficiency, a conventional wet type flue gas desulfurization apparatus typically has complicated structure similar to the one shown in FIG. 4. Flue gas leaving, for example, a steam generator passes an air preheater and an electrostatic precipitator, and is introduced into the wet type flue gas desulfurization equipment by means of an induced draft fan (IDF). The air preheater heats combustion air, while the electrostatic precipitator removes dust particles of coal ash etc. from the flue gas.
The flue gas leaving the electrostatic precipitator is pressurized by a boost-up fan (BUF), passes a gas-gas heater (GGH) in which the flue gas is cooled down while the flue gas having been treated for desulfurization is heated up, and the flue gas is introduced into an absorption tower or absorber column. The flue gas treated in the absorber and heated up in the gas-gas heater becomes lighter and is discharged into the higher atmosphere through a high stack by the effect of draft.
On the other hand, after preparation in the limestone slurry tank, a lime slurry is introduced into the absorption tower, in which it reacts with sulfur oxides including SO.sub.2 present in the flue gas resulting in a gypsum slurry retained at the bottom of the absorption tower. The absorption tower is provided with grid type or other kind of packing layers. The lime slurry flows downward through the packing layers. The flue gas flows co-currently with the absorbent slurry through the bed of packing where the gas and the liquid phases are contacted and the lime component of the slurry reacts with the SO.sub.2 content of flue gas.
As a subsequent step, water is removed from the gypsum slurry in a centrifugal separator and gypsum is produced. The waste solution or water removed from gypsum slurry in the centrifugal separator is discharged after treatment in a waste water treatment facility.
As described above, in case of conventional wet type flue gas desulfurization apparatuses, a high sulfur removal of 90 to 95% is achieved taking environmental issues into consideration, and the treated flue gas is dispersed into the higher atmosphere.
However, to achieve a high degree of sulfur removal with conventional technique both construction of the process and structure of the individual units are complex. For this reason, both equipment cost and operation cost are high, and operation requires high technical skills.
Therefore, when a lower capability of desulfurization is acceptable, especially when there is no need to produce a high purity gypsum by-product, the conventional wet type flue gas desulfurization apparatus with superior desulfurization capability may not be economically adequate if equipment and operation costs are taken into consideration. Furthermore, since high operational skills are required, such an apparatus cannot be operated with high efficiency if operators are under-trained and they cannot carry out maintenance jobs well.
In addition, because of the complexity of the system and structure, conventional apparatuses are difficult to add to the flue gas generating apparatus of existing thermal power plants and other facilities.
At present, in industrially developing countries where rapid industrialization is taking place, problems of environmental pollution caused by flue gas, etc. has to be solved urgently. In addition, since population density in such countries is comparatively low, a rapid improvement in the environmental conditions may be achieved even by using desulfurization apparatuses with relatively lower efficiency. Furthermore, there is a strong demand for inexpensive equipment since these countries are not in abundance of financial resources. Moreover, it has become an important issue in these countries to have desulfurization apparatuses that can be installed on existing air-polluting systems such as thermal power plants.
Thus, the conventional wet type flue gas desulfurizing apparatus with high desulfurization efficiency cannot provide a quick as well as both technically and economically satisfactory solution to the flue gas treatment problem in industrially developing countries. There is a strong demand to realize a wet type flue gas desulfurizing apparatus characterized by a relatively low desulfurization efficiency of 70 to 90%, simple construction, and easy operation.